BUG#20598

Fix race between cleanup and thread kill at server shutdown that would
sometimes prevent proper cleanup, leading to Valgrind warnings.

sql/mysqld.cc

@@ -1266,13 +1266,13 @@ void clean_up(bool print_message)
           MYF(MY_WME | MY_FAE | MY_ALLOW_ZERO_PTR));
   DBUG_PRINT("quit", ("Error messages freed"));
   /* Tell main we are ready */
+  logger.cleanup_end();
   (void) pthread_mutex_lock(&LOCK_thread_count);
   DBUG_PRINT("quit", ("got thread count lock"));
   ready_to_exit=1;
   /* do the broadcast inside the lock to ensure that my_end() is not called */
   (void) pthread_cond_broadcast(&COND_thread_count);
   (void) pthread_mutex_unlock(&LOCK_thread_count);
-  logger.cleanup_end();
 
   /*
     The following lines may never be executed as the main thread may have